Conventionally, for example, as represented in JP-A-2004-253911, ultrasonic sensors equipped with a plurality of reception-purpose piezoelectric vibrating elements are known in the technical field.
The ultrasonic sensor indicated in JP-A-2004-253911 has been equipped with a plurality of piezoelectric vibrating elements and a single vibration case for storing thereinto these piezoelectric vibrating elements. These plural piezoelectric vibrating elements contain at least one transmission-purpose piezoelectric vibrating element and at least two reception-purpose piezoelectric vibrating elements. Then, a plurality of storage concave portions having bottom planes along an incoming/outgoing radiation plane have been provided in the vibration case, and the piezoelectric vibrating elements have been contacted/arranged on the bottom planes of the corresponding storage concave portions. Also, a partitioning concave portion has been formed on a portion of the vibration case, which is located between the storage concave portion where the transmission-purpose storage concave portion has been formed, and the storage concave portion where the reception-purpose storage concave portion has been formed.
On the other hand, as methods capable of detecting azimuth of an obstruction, generally speaking, it is known that such a detection method for detecting the obstruction based upon a phase difference of reception signals of the respective reception-purpose piezoelectric vibration elements can have higher detecting precision than another detection method for detecting the obstruction based upon a time difference of the reception signals of the respective reception-purpose piezoelectric vibrating elements. For example, assuming now that a frequency of an ultrasonic wave is 40 KHz (namely, wavelength λ being 8.5 mm), generally speaking, a dimension of a vibrating plane required for an ultrasonic sensor is selected to be approximately 10 mm, while considering a rigidness (namely, anti-shock characteristic with respect to jumping stone) of a vibrating plate (namely, portion of vibration case where piezoelectric vibrating elements have been contacted/arranged). The above-described vibrating plane implies such a plane which is vibrated by vibrations of the piezoelectric vibrating elements and/or of reflection waves. Also, it is preferable that adjacent vibrating planes have been separated from each other in an acoustic technical field. As a consequence, in the case of the above-described ultrasonic sensor disclosed in JP-A-2004-253911, a distance between the vibrating planes (distance between centers) corresponding to the adjacent reception-purpose piezoelectric vibrating elements becomes such a value exceeding 10 mm, and thus, exceeds the wavelength of the ultrasonic wave in a direction along the incoming/outgoing radiation plane. In other words, even when the azimuth of the obstruction is tried to be detected based upon the phase difference between the plural reception-purpose piezoelectric vibrating elements, the ultrasonic sensor cannot detect the obstruction over a wide range, but only over a narrow range. As to this wide range, for instance, such a range may be conceived which is defined by ±90 degrees (namely, 180 degrees while vibrating plane is set as center) along the horizontal direction with respect to a road plane. To the contrary, another technical idea may be conceived by which the vibrating plane is reduced, so that the wide range may be detected. However, in order to maintain frequencies, the thickness of the vibrating plate must be made thin, which may cause the rigidness of the vibrating plate to be lowered. As a result, it is practically difficult to secure the anti-shock characteristic.
Also, when the ultrasonic sensor disclosed in JP-A-2004-253911 is mounted on, for example, a bumper of a vehicle, at least the incoming/outgoing radiation plane of the vibration case is exposed via a through hole formed in the bumper to an exterior portion of the vehicle. This incoming/outgoing plane contains rear planes of bottom planes of the storage concave portions and the portions between the respective storage concave portions. In other words, the portion exposed to the exterior portion of the vehicle becomes large, which may deteriorate attractive looks.
Thus, it is required to provide an ultrasonic sensor and an obstruction detecting apparatus equipped with the ultrasonic sensor capable of detecting azimuth of an obstruction based upon a phase difference over a wide range without reducing an anti-shock characteristic, while attractive looks thereof are improved.
Further, conventionally, for example, as represented in JP-A-63-243783 and JP-A-10-224880, ultrasonic sensor apparatuses equipped with the following arrangements are known in the technical field. That is, the ultrasonic sensor apparatuses contain a plurality of waveguides; ultrasonic elements (ultrasonic wave transmitters, ultrasonic wave receivers and ultrasonic vibrating elements) are arranged at one end of each of these waveguides; and ultrasonic waves are transferred via the waveguides.
As previously described, in an ultrasonic sensor apparatus having such an arrangement that an ultrasonic element is arranged at one end of each of these waveguides, the other end of each of these waveguides on the arranging sides of the ultrasonic elements is opened. As a result, for example, when the conventional ultrasonic sensor apparatuses are mounted on moving objects such as vehicles, there are certain risks that foreign articles such as stones, water, sand, and mud are penetrated into the waveguides. Then, the following problems may be conceived: That is, since the foreign articles collide with the ultrasonic elements, these ultrasonic elements may be damaged, and also, the foreign articles located within the waveguides may give adverse influences to propagation of ultrasonic waves. However, reflection waves caused by reflection articles (e.g., obstructions) present outside the ultrasonic sensor apparatuses are changed based upon the below-mentioned aspects, namely, whether or not reflection articles are present; distances separated from the reflection articles; sorts (surface concaves/convexes etc.) of the reflection articles. For instance, there are some possibilities that any reflection wave cannot be detected not only when any reflection article is not present, but also even when a reflection article is present. As a consequence, even when reception signals caused by reflection waves are brought into such a condition which is different from the normal reception condition (for instance, such a reception condition that peak value is low), and/or even when reception signals caused by reflection waves are brought into such a condition that these reception signals cannot be detected, it is practically difficult to discriminate these causes from each other, namely, the abnormal condition which is caused by the reflection articles, or the non-detection condition caused by that the ultrasonic sensor apparatus itself is under abnormal condition.
Thus, it is required to provide an ultrasonic sensor apparatus capable of diagnosing whether or not the own ultrasonic sensor apparatus is brought into an abnormal condition.